Menisci play an important mechanical role in the knee, including load transmission, energy dissipation, joint congruity and stability. It is now widely recognized that loss of meniscal integrity is an important contributor to the development of degenerative changes and osteoarthrosis. This has lead to an emphasis on preservation of meniscal tissue in the setting of meniscal repair as well as augmentation techniques used to facilitate meniscal healing. Clinical evaluation and post-operative management in the setting of meniscal repair is clearly challenging and variable from patient to patient. This application proposes to perform a study that will implement novel MR pulse sequences (ultrashort time to echo (UTE) techniques) that are able to acquire signal intensity from meniscal tissue, not possible on standard clinical MR sequences. In so doing, in our first aim, we will compare the accuracy of novel and conventional MR pulse sequences for characterizing tissue structure using a histopathologic reference standard. Our hypothesis is that novel ultrashort time to echo (UTE) sequences will be more accurate in evaluating meniscal structure. Quantitative MR techniques have been introduced in the literature over the past several years that are reported to reflect the biochemical content of tissue. These include, among others, T2 mapping (reflection of collagen) and T1 rho mapping (reflection of proteoglycan). In our second aim, we propose to compare the relationship between standard clinical quantitative T2 and T1 rho techniques with those performed with the UTE technique, using biochemical, biomechanical and histopathologic reference standards. Our hypothesis is that MR sequences that can acquire signal from meniscal tissue (UTE technique) will correlate more strongly with changes in collagen and proteoglycan integrity. In our third aim, we will apply the aforementioned techniques in an in vitro human meniscal and in vivo ovine model of meniscal repair implementing histolopathologic and biomechanical reference standards. Our hypothesis is that quantitative MR sequences will allow non-invasive tissue characterization of the healing response (both structural and biomechanical) in the setting of meniscal repair. In our final aim, we will translate the novel MR pulse sequences to a cohort of patients that have undergone primary meniscal repair with interrogation at 1, 3 and 4 months post-meniscal repair. We will also get a pre- MRI prior to the surgical procedure. We will use a clinical assessment tool as a reference standard. Our hypothesis is that quantitative MR sequences can successfully be translated to the clinical setting where they can monitor tissue response in the setting of meniscal repair.